Left 4 Dead goes live on Steam

Valve has thrown the switch and released Left 4 Dead to the waiting hordes of Steam users eager to get cracking on the PC version.

Left 4 Dead is a co-operative first-person shooter in which four players fight their way through four campaigns of rampaging zombies.

Each player gets a big old assault weapon and an unlimited-fire pistol, along with a med-pack, before facing off with hundreds of zombies, which appear in different patterns from different places depending on the whim of Valve's "AI director".

The key to survival is coordinating with your human allies to save one another from being overrun, and restocking at safe rooms along the way to a final extraction point, which then comes under siege. Also, don't shoot the witch.

On the flipside, another team of four people can also play as the infected "boss" types - a hulking tank character, a pouncing hunter, an exploding fat man called the boomer and the smoker with a noose for a tongue.